1. Field of the Invention
The present invention relates to an ultrasonic bonding method of electric wires in which electric wires to be bonded are intersected with each other, and intersected portions are bonded to each other by ultrasonic vibration.
2. Description of Related Art
In an ultrasonic bonding of coated electric wires, the coated electric wires are subjected to ultrasonic vibration and pressurizing force at the same time, thereby bonding the wires to each other (see Japanese Patent Application Laid-open No. H7-212036). The electric wires can be bonded to each other using the ultrasonic bonding method (see Japanese Patent Application Laid-open No. H9-29445).
FIG. 1 shows one example of an ultrasonic bonding apparatus 1. In the ultrasonic bonding apparatus 1, a horn 1b projects from an oscillator 1a in a horizontal direction, and a horn-side chip 1c is fixed to a tip end of the horn 1b. An anvil-side chip 1d is opposed to the horn-side chip 1c, and the anvil-side chip 1d is fixed to a base 1e. When intermediate portions of the electric wires 2 and 3 are to be bonded to each other, the electric wires 2 and 3 are intersected with each other, their intersected portions C are sandwiched between the horn-side chip 1c, and the anvil-side chip 1d and in this state, the horn-side chip 1c, is subjected to ultrasonic vibration, thereby bonding the intersected portions C. At that time, a vibration direction X of the ultrasonic vibration input to the horn-side chip 1c is a projecting direction of the horn 1b. 
In the conventional ultrasonic bonding method of electric wires, however, it is general that the one electric wire 2 is disposed in a direction perpendicular to the vibration direction X at right angles, and the other electric wire 3 is disposed in the vibration direction X as shown in FIG. 2. Therefore, when conductors 2a and 3a are stranded wires, when the conductors 2a and 3a are to be bonded after insulators 2b and 3b of the electric wires 2 and 3 are molten and removed as shown in FIG. 3, a rotation (rolling) direction of the conductor 2a intersecting the vibration direction X at right angles and a vibration input direction coincide with each other. Thus, the vibration energy of the ultrasonic vibration adversely escapes as rotation of the conductor 2a, and the vibration energy can not be transmitted to a surface of the conductor, which deteriorates bonding effect. If attempt is made to increase the pressurizing force against the horn-side chip 1c to suppress the rotation of the conductor 2a, the thin conductor 2a is cut by the excessive pressurizing force.
It is an object of the present invention to provide a ultrasonic bonding method of electric wire in which when intersected portions of electric wires are connected by ultrasonic vibration, vibration energy of the ultrasonic vibration can be transmitted to a surface of a conductor without exerting excessive pressurizing force, and bonding efficiency the conductors can be enhanced.
A first aspect of the present invention provides an ultrasonic bonding method of electric wires wherein electric wires are intersected with each other at right angles such that the electric wires are inclined with respect to the vibration direction of ultrasonic vibration through 45xc2x0 or about 45, intersected portions of the electric wires are set between a horn-side chip and an anvil-side chip in a pressurized state, and ultrasonic vibration is input to the intersected portions, thereby bonding the electric wires to each other.
In this case, since the ultrasonic vibration is applied to the intersected portions of the electric wires from a direction inclined with respect to the electric wires through 45xc2x0 or about 45xc2x0, rotation of the conductors of the electric wires are prevented or suppressed, the ultrasonic vibration energy can efficiently be transmitted to the surfaces of the conductors, and the bonding efficiency between the conductors can be enhanced.
According to a second aspect of the invention, in the above ultrasonic bonding method of electric wires, the horn-side chip and the anvil-side chip have set surfaces, and at least the set surface of the horn-side chip is provided with an uneven portion formed with grid-like grooves which are in parallel to and perpendicular to the vibration direction.
In this case, even if the electric wires are inclined, the intersected portions of the electric wires can be sandwiched between the horn-side chip and the anvil-side chip without slip and thus, the ultrasonic vibration energy can efficiently be transmitted to the intersected portions of the electric wires.